Organic syntheses via transition metal complexes. 109. Transfer of carbeneligands from group VI metals to rhodium as the key step of a rhodium-catalyzed reactivity enhancement of Fischer carbene complexes

Vinylcyclopentadienes 5a-h were obtained under mild conditions at 20 degree sC in 71-78% yields by a rhodium-catalyzed condensation of 1-alken-3-ynes 4 a,b with 4-amino-1-metalla-1,3-butadienes (OC)(5)M=C(OEt)CH=C(Ph)NR2 (3; M = W, Or). The key step of this transformation involves formation of a rhoda octatetraene (type B) by transmetalation and a subsequent insertion of the alkyne unit into the Rh=C double bond. RhCl3. 3H(2)O in CH3OH was found to be a simple and most efficient (pre)catalyst of this reaction. [(COD)RhCl]( 2) and [(OC)(2)RhCl](2) have been also successfully applied as precatalysts .